Filter and method of making same

ABSTRACT

An odor-removing filter approaching the carbon- particle loading of a filled filter may be formed by spraying or roll coating the adhesive against one or more faces of a porous, fibrous, air-permeable mat, depositing carbon particles or other odor-removing particles of a size to compliment the void size of the mat on the adhesive coated face or faces of the mat and then driving the particles into the mat and thereafter curing the adhesive to lock the particles into the mat. The adhesive bond of the particles to the mat is improved by working the particles against the adhesive- coated fibers. An overspray of an adhesive may also be utilized to further improve the retention of the particles. So-called &#34;clean filters&#34; may be produced according to the method disclosed, wherein a white, fibrous mat has carbon particles loaded on one face while the opposite face appears white or &#34;clean&#34;. An indicator filter notifying the user when the filter becomes grease laden may also be formed following the methods used herein.

RELATED APPLICATIONS

This application contains the disclosure of U.S. application Ser. No.000,176 field 20 May 1988 and is a continuation-in-part thereof.

FIELD OF INVENTION

This invention relates to odor-removing filters and the disclosureincorporates by reference the disclosure of U.S. Pat. No. 4,227,904, andU.S. Pat. No. 4,699,681.

BACKGROUND OF INVENTION

In U.S. Pat. No. 3,019,127 a glass fibrous mat made of fibers measuringfrom approximately 20-25 microns is sprayed with an adhesive, carbonparticles of 12 to 50 mesh are sprinkled on the pad, the pad vibrated todistribute the particles and the adhesive cured to adhere the particlesin the mat. The method results in a relatively low carbon particleloading, i.e., on the order of 4 percent of particulate material perunit volume of pad. In U.S. Pat. No. 4,227,904, carbon particlesmeasuring 12/28 to 4/6 (Tyler Screen Series) are glued to the face of aperforated substrate to provide a layer of particles on the substrate.This results in a medium loaded product. A highly loaded, thin-bedfilter has been made by D-Mark, Inc. of Mt. Clemens, Mich. and otherswherein the space between two perforated sheets is filled with loosecarbon particles. This results in a high capacity filter, but theparticles tend to settle resulting in channeling and shedding of carbondust. As used herein, the term thin-bed filter refers to a filter havinga bed or substrate measuring in thickness anywhere up to two inches.

It has been a long-sought objective to provide an odor-removing thin-bedfilter with reasonably high carbon loading, low carbon shedding and noinduced channeling at a low unit cost. In some instances, as for thecommercial/industrial filter market, a highly efficient, high-capacityfilter is desired, while for the range hood and appliance markets asomewhat less efficient and lower capacity filter may suffice. Inproviding filters for these two markets, allowable pressure drops mustbe adhered to. For example, in the range hood market, this pressure dropshould preferably not exceed 0.15 inches of water column, while in thecommercial/industrial market, 0.3 inches is typically allowable.

In the manufacture of the filter according to U.S. Pat. No. 4,227,904,relatively large, odor-removing, pelletized particles are employed suchas 6/8 mesh (Tyler Screen Series). This size pelletized material hasbecome difficult to acquire and substitute materials have been difficultto reliably adhere to the filter substrates. As the filter made underU.S. Pat. No. 4,227,904 was particularly adapted for manufacture withthe 6/8 pellet, the need has arisen to find other approaches to themanufacture of thin-bed type filters.

In addition, there has been a need to provide a combination odor andgrease removing filter that will visually indicate when it has becomegrease laden and should be replaced.

In seeking to provide suitable filters for both the range hood/applianceand the commercial/industrial markets at the lowest cost, it has becomedesirable to provide a method of manufacture that utilizes readilyavailable granular carbon and is sufficiently flexible so filtersespecially designed for these different markets may be produced withoutrequiring separate dedicated production lines. This has lead to thedesirability of a filter wherein the odor-removing media is so suspendedin the air stream that greater or lesser quantities of the media may beprovided (in accordance with the different market requirements) bysimple changes in the method of filter manufacture.

SUMMARY OF INVENTION

We have discovered how to provide a filter having carbon particlessuspended in the air stream in a quantity approaching that of aconventional filled filter but without the disadvantages associatedtherewith such as shedding or channeling or the high pressure dropassociated with some filled-filter designs. This is accomplished bysuspending the carbon particles in a substrate which is formed of aporous fibrous air- permeable mat having a denier of from 3 to 400,spraying the mat with an adhesive sufficient to penetrate as far throughthe mat as the carbon particles are to be suspended, then depositingcarbon on the mat and driving them thereinto and thereafter curing theadhesive to lock the particles in the substrate. If desired, the odor-removing particles may extend completely through the thickness of thesubstrate.

We have found that the particles may be more effectively locked in thesubstrate, in some cases, by applying a second coating of adhesivethereto. In addition the thickness of the final substrate may becontrolled by passing it through sizing rollers. We have also discoveredthat a substantial improvement in the state of the art may be providedby matching the particle size to the void size in the substrate. Forexample, a larger denier, more open mat may be filled with largerparticles whose size tend to fill the voids between the fibers of themat. We have further found that the effectiveness of the adhesive bondmay be improved by working the particles against the adhesive-coatedfibers. Techniques for effecting such working are disclosed.

Methods of making thin-bed type filters which are capable of producing amore heavily loaded filter than that shown in U.S. Pat. No. 3,019,127 ora more uniform and more securely attached carbon layer than that in U.S.Pat. No. 4,227,904, are herein disclosed. In addition, a basic designconcept for the filter enables manufacture of filters for both the rangehood/appliance market and the commercial/industrial markets utilizingthe same production line with simple changes to accommodate theparticular end result desired. According to the method, a poroussubstrate is coated on one or both sides by an adhesive spray,odor-removing particles are deposited on one or both sides and thendriven into the substrate, the adhesive is cured and the carbon loadedsubstrate is assembled into a filter. Following the teaching herein,utilizing 6/12 carbon particles in a 250 denier unwoven polyester mat(substrate) carbon loadings approaching one pound per square foot in a1/2 inch thick finished substrate have been achieved. This is believedto be substantially greater than any loading heretofore achieved in theprior art. The odor-removing particles are driven into the substrateeither by application of an air stream impinging on the particles anddriving them into the substrate, or they may be pressed into thesubstrate through the application of a roller pressing against them orby a combination of an air stream and a roller. Pressing of theodor-removing particles into the substrate by the roller has been foundto improve the adhesive retention of the particles in the substrate.Excess particles are removed from the substrate by application of an airstream directed against them.

Where it is desired to further improve retention of the odor-removingparticles in the substrate, the substrate may be sprayed with a secondadhesive coat (overcoat) before the substrate is passed through thecuring stage to cure the adhesive thereon. This second coat of adhesivespray serves to lock the odor-removing particles in the substrate. Thesecond coat follows driving of the particles into the substrate and/orremoval of excess particles from the surface of the substrate.

The adhesive is cured as by passing the substrate through an oven.Adjacent the outlet of the oven, the thickness of the substrate may besized by passing the substrate between sizing rollers.

Where both sides of a substrate are to be filled with the odor-removingparticles, the process is preferably carried out by first coating oneside of the substrate, depositing the odor-removing particles thereonand driving them thereinto, removing excess particles and then curingthe adhesive. Thereafter the process is repeated on the opposite side ofthe substrate.

A so-called "clean" filter may be produced according to the methodherein disclosed. A white fibrous mat may have one side sprayed withadhesive and the odor- removing particles deposited thereon andpartially driven thereinto, excess particles removed, and the adhesivecured. This will result in a filter pad having one side which is whiteor "clean" while the opposite face is covered by the odor-removingparticles. By placing such a substrate in a filter assembly so that thewhite side is exposed to view, a particle-removing filter having anodor-removing capability is provided.

Another type of so-called "clean" filter which is also an "indicator"filter may be provided by coating one side of a light colored or whitefibrous substrate with an ink pattern according to the teaching ofGerman Patent 27 08 435. The printed surface of this substrate is thencoated with an adhesive spray insoluble with respect to the aforesaidink, and odor-removing particles are then deposited on theadhesive-coated surface, and may then be driven into the substrate andthe adhesive cured. This will provide a particle and odor-removingindicator filter.

A further filter embodiment made according to the method hereindisclosed comprises an expanded metallic layer which has a coating ofcarbon adhered to the face thereof. The carbon is attached to thissubstrate following the teachings of the method herein disclosed.

In further experimentation with the methods of filter manufacture hereand above mentioned, it has been discovered that effective particleretention in the porous, fibrous air-permeable mat may be accomplishedwithout spraying adhesive on the mat, by roll coating the adhesive ontothe mat utilizing a conventional roll coating applicator of the typedisclosed in U.S. Pat. No. 4227904. Utilizing a roll coater it has beenfound that savings on the amount of adhesive required may be effected upto 50% or more as compared with the adhesive used in the sprayingtechniques herein disclosed. This not only has resulted in substantialcost savings, but obviated problems of water and air pollution and theaccompanying health concerns. In addition it has been found that rollcoating the adhesive onto the substrate has the effect of working theadhesive down into the substrate and working the adhesive against thefibers of the substrate to assure the coating of them so that theparticulate material is better adhered to the fibers.

It has also been discovered that utilizing a roll coating application ofadhesive to the substrate and a means for working the particles downinto the substrate, such as the air driver or roll driver hereindisclosed, the over spray or second spray application of adhesive to thesubstrate to lock the particles in the substrate is unnecessary. Testhave shown that utilizing the roll coating and either the air driver orroll driver, the particles are securely locked as effectively as whenthe adhesive was applied and then the substrate over coated utilizingadhesive sprays.

In addition it has been discovered that it is unnessary to substantiallythoroughly cure the adhesive but rather it is only necessary to cure itsufficiently so that the substrate with it's particulate loading may behandled and to permit the curing to continue as the substrate is furtherprocessed, as for example, during packaging and inventory storage or thelike.

Where it is desired to fully load a substrate, the adhesive is firstapplied by the roll coating technique, the particulate media applied tothe substrate and worked thereinto by the driver, the adhesive thenpartially cured to render it non-tacky and handable, the substrate isthen inverted and the process repeated on the opposite face. Such willresult in loading the substrate completely there through with the odorremoving particulate.

It has also been discovered that utilizing the method and structuresherein disclosed that filters may be created which are useful for airtreatment other than simply odor removal. For example, Zeoliteparticulate will absorb ethylene and when air is filtered through asubstrate loaded with Zeolite in conjunction with the storage of foodproducts, spoilage may be substantially retarded. Similarly, activatedAlumina impregnated with potassium permanganate will absorb ammonia andformaldehyde more effectively than will carbon thus utilizing activatedAlumina particulates in a substrate of the character herein disclosedwill result in a filter that will be very effective in absorbing ammoniaand formaldehyde from an air stream passing there through.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a processing line embodying the methoddescribed herein;

FIG. 2 is a cross-sectional view through a substrate being processed inthe spraying station of FIG. 1;

FIG. 3 is a cross-sectional view through a substrate being processed inthe particulate filling station of FIG. 1;

FIG. 4 is a cross-sectional view through a mat having odor-removingparticles driven thereinto and excess particles removed therefrom by anair driver;

FIG. 5 is a cross-sectional view through a substrate having theodor-removing particles extending substantially half-way therethroughand manufactured according to the method shown in FIG. 1;

FIG. 6 is a cross-sectional view through a substrate manufacturedaccording to the teaching of FIG. 1 and showing the odor-removingparticles extending substantially uniformly through the thickness of thesubstrate;

FIG. 7 is a cross-sectional view of a substrate as shown in FIG. 6 withthe same being enclosed within an air-permeable envelope or scrim; FIG.8 is a cross-sectional view through what we have termed as a "clean"odor-removing filter;

FIG. 9 is a cross-sectional view through a perforated, self-supportingsheet coated with odor-removing particles according to the methoddisclosed herein;

FIG. 10 is a cross-sectional view through a substrate being processedthrough a modified form of the particulate filling station of FIG. 1;

FIG. 11 is a cross-sectional view through a substrate being processedaccording to a still further modification of the method shown in theparticulate filling station of FIG. 1;

FIG. 12 is a cross-sectional view through a non-woven polyester padhaving odor-removing particles adhered to but one face thereof;

FIG. 13 is a modified form of "clean" filter; which also is an"indicator" filter manufactured according to the methods hereindisclosed;

FIG. 14 is a cross-sectional view through an expanded metal substratethrough which odor-removing particles have been adhered according to themethods herein taught;

FIG. 15 is a cross-sectional view through a modified form of the filtershown in FIG. 7;

FIG. 16 is a schematic view of a modified form of processing lineembodying a modified method described herein;

FIG. 17 is a plan view of a filter structure embodying a further form ofthe invention;

FIG. 18 is a cross-sectional view taken on the line 18--18 of FIG. 17;

FIG. 19 is a cross-sectional view similar to FIG. 18 but showing afilter structure which is not encased within a filter frame;

FIG. 20 is a cross-sectional view similar to FIG. 18 but showingdifferent form of substrate arrangement and without a filter frame.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 6 a porous, air-permeable, non-woven, fibrous substrate S hasbeen filled with odor-removing particulate media 22, adhesively securedin the substrate. The media has been shown as being substantiallyuniformly distributed over both of the opposed faces 24 and 26 of thesubstrate and throughout the thickness T of the substrate. The filter ofFIG. 6 may find particular utility in industrial or commercialapplications where a greater pressure drop can be tolerated and agreater capacity is desired. The process herein disclosed allows forvarying the amount of particulate media filling the substrate not onlyas between a distribution partially or completely through the thicknessT, but also as to the density of the loading. For example, in theembodiment of FIG. 6, the filling may be on the order of from 50 gramsto 355 grams of particulate per square foot of substrate where thefinished substrate is approximately 1/2 inch thick. The amount ofloading depends on variations in the method employed in the manufactureas well as the particulate size and the character of the substrate. Asmuch as 1 pound (454 grams) of particulate per square foot of substrate(nominally 1/2" substrate thickness) has been achieved and up to about500 grams appears feasible. Comparing particulate loading of the filterof FIG. 6 with the loading of a filled filter of comparable thickness,between 75 percent to 80 percent by weight has been achieved inpre-production testing. A very light weight filter may be made utilizinga light denier fibrous, non- woven mat of, for example from 3 to 100denier and a density of from 1 to 6 ounces per square yard. Filling mayutilize odor removing media on the order of 20/50 carbon (U.S. Mesh) to-400. The percent of loading may lie in the range of from 8.8% by volumeto 88%.

In preparing a filter such as shown in FIGS. 5 and 6, a non-wovenfibrous mat substrate having a fiber denier of from 3 to 400 may beutilized. For example, a 250 denier fiber with a nominal thickness of1/2 inch and a weight of 10 to 28 grams per square foot is placed on theupstream end 32 of a conveyor line shown in FIG. 1 with one of theopposed faces disposed upwardly. Mats move along the line in thedirection of arrow D passing through a series of stations where varioussteps in the method of manufacturing the filter are performed. The firststation is the spraying station 34. It comprises a water trough 36containing an adhesive entraining water bath disposed below adhesivespray nozzles 38, which may be model No. 61 manufactured by BinksManufacturing Co. of Franklin Park, Ill. and which are mounted toreciprocate back and forth across the substrate as it passes through thestation. The bath will catch overspray of adhesive. Station 34 alsoincludes a conveyor 40 having an upper run 40' adapted to support thesubstrate to move it through the station and a return run 40" which dipsdown into the water bath. The spray nozzles may be housed in a spraybooth with a suitable exhaust system (not shown) for removing adhesiveaerosols. Adhesive is delivered to the nozzles to emit a spray that willpenetrate a substrate to be filled with the odor-removing particulate.For example, at 30-55 PSIG adhesive pressure and 20-65 PSIG air pressureat the nozzles, a conveyor speed of 5-35 feet per minute and the nozzlesbeing disposed approximately 11-12 inches from the mat, the substratefibers may be wetted with the adhesive to somewhat greater than one-halfthe thickness of the mat. Depth of penetration of the adhesive into themat will be dictated by the nature of the filter to be made, i.e., ifthe odor-removing particulate media is to extend substantially half waythrough the mat, then the spray should extend at least that far. Where afilter of the nature shown in FIG. 6 is to be manufactured, the sprayshould extend substantially half way through the thickness of thesubstrate so that upon inverting the substrate and passing it againthrough the spray station 34, the opposite face and remaining depth ofthe substrate may be wetted.

In FIG. 2 the upwardly disposed face 24a, of the substrate S is shownbeing sprayed with the adhesive A from the spray nozzles 38 whichreciprocate back and forth across the substrate. The adhesive is shownat A' on the substrate fibers and as having penetrated substantiallyone-half the way through the substrate.

Following application of the spray, the substrate S is moved to theparticulate filling station 44. Such station comprises a hopper 46containing the particulate odor-removing media to be loaded into thesubstrate. A hopper of conventional construction provided with a mediadischarge slot in its lower end is disposed above substrates passingthrough the station on the conveyor. The filling station includes itsown conveyor 48 which is adapted to receive on its upper run 48'substrates S delivered by the conveyor 40 and moves the substratesthrough the filling station. Beneath the conveyor 48 is a media catchtrough 50 for catching media which is not deposited on or does notremain on the substrates for recycling through the hopper. As thesubstrates pass beneath the nozzle 52 of the hopper the particulatemedia is dropped onto the upwardly disposed face of the substrate touniformly coat the same as the substrate passes beneath. FIG. 3 showsthe upwardly disposed face 24a having been loaded with the particulatemedia from the nozzle 52 of the hopper. Particulate media 22 builds upon top of the substrate as it issues from the nozzle 52 and some of theparticulate will sift down into the substrate as shown in FIG. 3 to theright of the nozzle 52. However, for the most part, the particulate willremain essentially on the surface of the substrate. The conveyor 48 hasan open substrate supporting surface enabling excess odor-removingparticulate to fall through the conveyor to the trough 50.

Downstream from the nozzle 52 is the particulate driving means generallyindicated in FIG. 1 at 54. The particulate driving means is shown inthree embodiments in this disclosure, the first being illustrated inFIG. 4 while the second and third are shown in FIGS. 10 and 11respectively. In each case the function of the particulate driver is topress the particulate media 22 down into the substrate and/or removeexcess media from the substrate.

Turning to FIG. 4 the particulate driver comprises an air pipe 56 whichextends transversely of the conveyor 48 in the filling station 44 spacedjust above the substrates on the conveyor upper run 48'. The upper run48' is of a sufficiently open character as to allow air and excess mediato pass downwardly therethrough. The air pipe is provided with a seriesof nozzles 58 which are simply 5/32" openings through the wall thereofdisposed at substantially 1/2-inch intervals. The pipe may bepressurized with a source of compressed air to approximately 60 PSI.This air is delivered from the nozzles and is directed against thesubstrates passing beneath the air pipe. As the air jets 59 impinge onthe particulate media 22, the jets drive the media down into thesubstrate and also serve to blow off from the top of the substrateexcess media. By controlling the force of the jets and the distance ofthe pipe from the upwardly facing surface of the media coated substrate,the amount of penetration of the particulate into the substrate can beregulated as can the amount of media blown off the substrate. By varyingthe rotated position of the pipe 56, the amount of odor-removing mediablown off the surface of the substrate or driven down into the substratemay be varied. Desirably, the effect of the air driver is regulated sothat a substantially uniform layer of particulate media lies on and inthe substrate just to the downstream side of the air pipe and excessmedia which is not in contact with adhesive coated fibers is blown offof the substrate. In FIG. 4 the particulate media 22' is shown at thedownstream side of the pipe 56 as generally uniformly covering theupwardly disposed face of the substrate and as having penetratedsubstantially half the thickness of the substrate. To the upstream sideof the air driver, the particulate 22" essentially lies on the upwardlydisposed face of the substrate in preparation for being driventhereinto.

In FIG. 4, the air-driver pipe 56 is shown with the jet openings 58being disposed substantially perpendicular to the substrate passingthere beneath. The rotated position of the pipe may be varied.

In FIG. 10 the second form of driver 54 is shown. Essentially itcomprises the driver of FIG. 4 designated by reference numeral 56asupplemented at its downstream side by a pair of rollers 58 and 58a. Therollers are mounted in suitable trunions at opposite sides of theconveyor and are driven by a suitable drive mechanism (not shown). Thesubstrates are fed between the rollers. The distance between the rollersis adjustable, but in a preferred embodiment the rollers are adjustedrelative to the substrate so as to press substantially halfway downthrough the substrate. The effect of rollers 58 and 58a, which may berotated at the same surface speed as that of the conveyor 48 is to pressthe particulate media down into the substrate. In addition, as therollers press the media down into the substrate, they work the mediaagainst the adhesive coating the fibers and effect a more secure lock ofthe substrate fibers and the media than simply the air driver alone inFIG. 4. Doctor blades (63 and 65) wipe the surface of the rollers tokeep them clear of accumulating adhesive.

In FIG. 11, the third form of particulate driver comprises a pair ofdriver rollers 61 and 61a of substantially the same character as thatshown in FIG. 10 disposed immediately .upstream from an air driver 56b.The rollers are arranged to press the particulate 22, which has beendeposited by the spout 52 upon the upwardly disposed surface of thesubstrate S, downwardly into the substrate and embed the same therein.The action of the roller 61 in pressing the particulate media into thesubstrate also serves to work the media against the adhesive on thesubstrate fibers to effect a good bond between the fibers and theparticulate media. As the substrate passes beneath the air driver 56bdownstream of the roller, excess media is blown therefrom. The drivershown in FIG. 11 will serve to embed the greatest amount of particulatemedia in the substrate as compared with the drivers of either FIGS. 4 or10.

Downstream of the driver means 54 is a second spraying station 62 forapplying a second or "overcoat" on the upwardly disposed face of thesubstrate. As with the spraying station 34, the second spraying station62 is provided with a reciprocating sprayhead 64 disposed within asprayhood 66 and adapted to reciprocate across the substrates as theypass through the station. A conveyor 68 of a construction similar toconveyor 40, and dipping on its return run into a water through 36',serves to transport the substrates through station 62. The purpose ofstation 62 is to spray the media filled surface of the substrate with asecond coating of adhesive to more effectively lock the odor removingmedia in or on the substrate by providing a coating of adhesive tobridge between the individual media particles and the substrate fibersto bond the same together. This second spraying station is utilized inthose instances where it is desired to obtain the most effective lockingof the odor removing media on or in the substrate. When the second coator over coat provided by Station 62 is utilized in combination with theair driver alone, as in FIG. 4, a more secure locking of the media inthe substrate is obtained than if the second coat was not applied. Thisdoes result in some lessening of the efficiency of the odor removingmedia, but does not appear to reduce significantly its capacity. If thesecond coat is omitted, but either the driver of FIG. 10 or the driverof FIG. 11 is utilized, the working of the particulate media effected bythe rollers improves the bonding action of the media with the substrate.The bond may not be quite as effective as with the second coatingafforded by station 62, but the efficiency of the media is not affectedas much. The most secure locking of the media to the substrate iseffected by utilizing the second coating provided by station 62 with thedriver of either FIGS. 10 or 11.

A substantial advantage of the second coat is in connection with theadhering of smaller size particles to the substrate. We have found thatby utilizing the second spray, it may be possible to eliminatealtogether the necessity of enclosing the particulate filled substratein an envelope or scrim to prevent shedding or contamination duringhandling or use of the filter. We have also found that the secondcoating is most effective in smaller size particles such as 20/50 (U.S.Screen). As the particle size increases the amount of adhesive that mustbe applied in the second coat to effect a more secure bond reaches thepoint where it adversely affects the efficiency of the odor removingparticulate.

Downstream from station 62 the substrates pass through a drying/curingstation comprising an oven 70 having a conveyor span 71 whose upper runreceives the substrates S from station 62 and conveys them through theoven. In the oven the adhesive is cured sufficiently so that uponemerging from the oven the substrates may be handled without the odorremoving media dislodging therefrom.

Downstream of station 74 is a tolerance determining or thickness sizingstation 76. This station comprises a pair of driven rollers 78 and78aextending transversely of the conveyor 72 and adapted to receivetherebetween the substrates emerging from the curing station andcompress the substrates a predetermined amount. The space between therollers may be adjusted to effectively squeeze the substrates apredetermined amount. As the substrates are hot as they emerge from theoven, the roller will serve to "set" the thickness of the substrates.

Downstream of the tolerance station as at the end 80 of the conveyor,the substrates are successively removed from the processing line forfurther handling. If it is intended to fill both sides of thesubstrates, the substrates will be returned to the upstream end 32 andreplaced on the conveyor with the unfilled side or face disposedupwardly for passage through the processing line. The steps previouslydescribed would then be repeated to provide a substrate which is filledfrom both sides with the odor removing particles. Utilizing the methodheretofore described and passing the substrate through the processingline twice to fill opposite faces 24 and 26 thereof, and using theparticulate driver of FIG. 11, it has been possible to provide a loadingin a 1/2 inch nominal final thickness substrate of substantially onepound of activated carbon per square foot of substrate.

In FIG. 7, the substrate S of FIG. 6, has been enclosed within a scrimenvelope 64 comprising upper and lower layers 64A and 64B which havebeen stitched together or otherwise secured around the periphery of thesubstrate as at 67. The scrim is an open mesh material through which airwill readily pass. The function of the scrim is to contain within theenvelope carbon which may become dislodged from the substrate. The scrimenvelope is particularly useful where the substrate has not beensubjected to the overcoat spray of station 62, nor the action of rollers58 and 58a or 60 and 60a.

If desired, a layer to filter airborne particles may be disposed insidethe envelope to overlie one or both of the faces of the substrate. Onesuch layer is shown in FIG. 15 wherein the filled substrate S' isenclosed within a scrim 64' with a particle filter 68 disposed withinthe envelope. The intended direction of air flow through this filter isas shown by arrow A. The particle filter pad 68 may be a fuzzy pad thatis intended to remove airborne particles before they reach theodor-removing substrate. A suitable pad is sold under the brand nameFILTRETE and manufactured by 3M Company of St. Paul, Minn.

In FIG. 8, there is shown what may be termed a "clean" filter. In thisembodiment a white (or light- colored) pad or substrate S ofapproximately 1/4 inch thickness of a non-woven, fibrous characterhaving fibers of from 3 to 40 denier and a density of from 2.0 to 6.0ounces per square yard, is sprayed on one surface with adhesive as inspraying station 34. Odor-removing media, such as activated carbongranules of 20/50 (U.S.) mesh, are deposited on the adhesively-coatedface of the substrate. The air driver of FIG. 4 then removes the excesscarbon particles to provide a generally uniform layer of carbonparticles on the pad approximately one particle thick. The pressure ofthe air supply to pipe 56 and the direction of the air jets is socontrolled that the carbon particles are not driven too deeply into therelatively thin substrate to essentially provide simply a thin coatingof the carbon granules on the surface as shown at 22A. The substratewith carbon thereon is then sprayed with a second coating of adhesive instation 62 and then passed through the curing oven to set the adhesive.The substrate would not normally be passed between the tolerance rollers78 and 78a, but rather would be directly packaged in a supporting frame.Air flow through this substrate would be in the direction of Arrow A inFIG. 8. This filter is intended to be used primarily in range hoods andto give the householder an indication when the filter is contaminatedand should be replaced because the clean appearance of surface 26A willbecome discolored by the entrainment of grease particles in the pad.

In FIG. 9, a substrate S_(a) comprises a perforated self-supportingsheet similar to those of U.S. Pat. No. 4,227,904. It is provided withperforations 70. The substrate is sprayed with adhesive as in sprayingstation 34 and odor-removing particles 22b are deposited thereon as instation 44 and excess particles are blown off the surface as by the airdriver of FIG. 4 to provide a generally uniform layer of carbonparticles approximately one particle thick. An overcoating of adhesiveis then applied as by station 62 and the substrate then passed throughthe drying/curing station 74. Such substrate need not be subjected tothe tolerance station 76 but may be removed from the end 80 forsubsequent use.

The second or overcoat provided by station 62 enables such a substrateto retain the odor-removing media thereon and in this respect, themethod herein disclosed represents an improvement on the method ofmaking a filter disclosed in U.S. Pat. No. 4,227,904, wherein thesubstrate is coated by a roller coating technique. The second orovercoat disclosed herein makes it possible to lock the odor-removingparticles on the substrate without resort to roller coating with theresulting product having a more uniform particulate loading withoutshedding.

FIG. 12 is a filter corresponding to that of FIG. 8 except thatfollowing deposit of the carbon particles and removal of the excesscarbon, a second adhesive coating is sprayed over the carbon coated faceof the substrate as in Station 62 to lock the carbon particles on thesubstrate. The filter is, of course, passed through the curing station.If desired, the substrate may be sized in thickness as by the roller 78.This substrate may be more dense than that of FIG. 8 where an increasedpressure drop can be tolerated and greater particle filtering action isdesired.

In FIG. 13 another type of "clean" filter is disclosed which is also an"indicator" filter, i.e., will indicate to the user when the filter hasbecome loaded with grease and should be replaced. A light colored orwhite fibrous non-woven substrate S_(c) is printed on one side 72 withan ink pattern such as disclosed in German Patent 27 08 435. This inkpattern may be printed on a face of the substrate in any suitablefashion. The ink itself should be of a color that contrasts with that ofthe substrate. It may be made up, for example, of 5 parts of greasesoluble (water insoluble) organic dye stirred with 5-10 parts of asuitable emulsifier having the property of dispersing grease soluble butnot water soluble dyes in water. Thereafter, 30 parts of a water solublebinder are stirred in until the mixture is homogeneous. The mixture isthen treated with 55 parts water and printed on the substrate face 72.The non-woven substrate S_(c) will function as a particle filter.

The substrate is then passed through the processing line shown in FIG. 1with face 72 disposed upward and the face coated with a spray of theadhesive in station 34, then coated with odor-removing particles inStation 44 and then passed beneath the air driver shown in FIG. 4 todrive the odor removing media down into the substrate and also removeexcess particles. A second or overcoating of adhesive is then applied instation 62 to the side 82 of the substrate to lock the odor-removingparticles on the substrate. Following this the substrate is passedthrough the curing or drying oven in station 74. The substrate may thenbe optionally passed through the tolerance station 76 to size thethickness of the pad. The substrate is then mounted in a suitable framewith the media covered face 72 disposed downstream so that the normalair flow is in the direction of Arrow A and the exposed face 75 will bethe one observed by the user. This type of filter is particularlydesirable for use in range hoods. As the substrate S_(c) becomesgrease-laden, the ink 73 will migrate toward the surface 74 and whenvisible to the user will indicate that the substrate has becomegrease-loaded and the filter is ready to be replaced. Of course, theodor-removing particulate 77 will remove the odors from the air streamas it passes through the substrate.

FIG. 14 shows an expanded metal substrate S_(d) on the face 79 of whichhas been adhesively secured a layer of odor-removing particulate 81. Thesubstrate S_(d) may be prepared by placing the substrate at the entryend of the processing line shown in FIG. 1 with the face 78 uppermost,and then sprayed with adhesive in the spraying station 34, the substratethen passed to station 44 where odor-removing particles are applied andthen passed beneath the air driver of FIG. 4. The air pressure isadjusted to remove only enough particulate so that a uniform dense layerapproximately one particle thick remains on the substrate surface asshown in FIG. 14. The substrate is then passed to station 62 where asecond or over coat of adhesive is applied to lock the particles on thesubstrate. The substrate is then passed through station 74 to dry orcure the adhesive. In the case of this type of substrate, the rollers 78and 78a are not utilized for sizing. The resultant substrate may beprocessed through the line once more to coat the opposite surface of thesubstrate in like fashion if desired. The substrate, thus prepared, maybe mounted in a suitable frame for use as a filter.

The substrates of FIGS. 2-8 may be formed of polyester, nylon,polypropylene or glass fibers. Other fibers, either natural or man-madeto meet the particular requirements of the intended use of the filtersmay be utilized. In addition, open cell polyurethane, or the like,reticulated foam may be utilized.

The adhesive to be used may be styrene acrylic latex, vinyl acetate,ethylene vinyl acetate, polyvinyl acetate, p.v.c. and acrylic latex, orother adhesives meeting the requirements for the use of the filter.

The odor-removing particles useful herein may be either activatedcarbon, activated aluminum impregnated with potassium permanganate,silica gel and the like. As used herein the term "odor-removingparticles" is also intended to cover oxidizing materials such asmanganese dioxide.

The scrim material shown in FIG. 7 may be spun bonded nylon orpolypropylene, knitted polyester, or woven fiber of a variety ofmaterials.

Examples of filters made utilizing the method disclosed herein are asfollows:

EXAMPLE 1

(a) A 1/4 inch nominal thickness polyester pad measuring 12 by 12 madeof a 32 denier non-woven fiber with a density of 2 to 3 ounces persquare yard was placed at the entry end of the processing line shown inFIG. 1 and passed through various steps as hereinafter detailed.

(b) In spraying station 34, the upwardly disposed face of the substratewas sprayed with an acrylic latex adhesive identified as UCAR 153,manufactured by Union Carbide Corporation having a viscosity of lessthan 500 cps. at 20'C. This adhesive was sprayed through a two-componentspray head with the air at 40 to 60 psig and the adhesive at 30 to 55psig at a distance of approximately 11 inches with the spray head, orheads, reciprocating across the pad. Between 20 and 30 grams of adhesiveper square foot was thus applied.

(c) Following the spraying of the upwardly disposed face, the substratewas passed to station 44 where 20/50 U.S. mesh activated carbonparticles in 30 to 60 activity was applied to the upwardly disposedadhesive sprayed face of the mat at the rate of between 30 to 55 gramsper square foot. A suitable carbon granule for this purpose is made bySorbtech, Inc. of Woodlands, Tex. Following application of the activatedcarbon, the substrate was passed beneath an air driver as in FIG. 4where air jets are directed downwardly at the substrate of sufficientforce to drive the activated carbon particles down into the substrateand at the same time blow off the excess particles. For this purpose theair pipe 56 may be of a 1 inch inside diameter with air holes of 5/32inch diameter spaced 1/2 inch apart and with an air pressure of 60 psig.The pipe is spaced 11/2 inches above the substrate.

(d) Following the air driver, the substrate was passed to the station 62where a second or overcoat spray was applied at the rate of 2 to 10grams per square foot of the same adhesive as was applied in station 34.The adhesive was sprayed using a spray head and at pressures similar tothose described in sub-paragraph (b) at a distance of approximately11/12 inches. The second coat bridged the particles and also bridgedbetween particles and fibers so that upon curing the adhesive theparticles are quite securely locked in the mat.

(e) The substrate was then passed through the curing station 74 where itwas raised to a temperature of 200° to 350° F. for a period ofapproximately 2 minutes. During this interval the water content of theadhesive was evaporated out. Following the oven, the filled substratewas passed through a sizing station similar to station 76 to size thethickness of the mat. Thereafter the filled substrate was mounted in asuitable frame for use as a filter.

EXAMPLE 2

(a) A filter was made according to the process described in Example 1,except after passing out of the curing oven in station 74, the substratewas re-entered in the processing line with its opposite or uncoated facedisposed upper-most and each of the steps thereafter repeated on theupwardly disposed face of the substrate. The pressure of the air driveron both passages through the processing line was selected so that thecarbon particles were driven substantially half way through thesubstrate with the result that the final product had the activatedcarbon distributed substantially uniformly through the entire thicknessof the substrate.

EXAMPLE 3

(a) A one-half inch nominal thickness, non-woven polyester pad measuringapproximately 12×18 and made of 200 denier fiber with a density ofbetween 4 and 9 ounces per square yard was entered at the upstream endof the processing line of FIG. 1.

(b) In station 34, the adhesive corresponding to that mentioned inExample 1 was applied to give a wet loading of approximately 25 gramsper square foot.

(c) At station 44 activated carbon measuring 6/12 U.S. mesh of 50 to 65activity was deposited at the rate of 160 grams per square foot. Thesubstrate was then subjected to the action of the air driver as insubparagraph (c) of Example 1, to drive the carbon particlessubstantially half way through the thickness of the substrate.

(d) The substrate was then subjected to a second coat as in station 62of 2 to 10 grams of adhesive per square foot of substrate.

(e) The substrate was then passed through the curing station 74 andfollowing such was subjected to the sizing in the tolerance station 76and its thickness (which has grown during processing) is reduced to 1-2.

EXAMPLE 4

(a) A substrate was made according to the process of Example 3 except noovercoat as in Station 62 was applied to the substrate. The finishedproduct emerging from the curing station 74 was enclosed in a non-wovenhighly porous scrim envelope to prevent shedding. The scrim materialfound suitable for this purpose is manufactured by James RiverCorporation, and has a denier of 3.5 and a density of 0.4 ounces persquare yard.

EXAMPLE 5

(a) A substrate was processed according to Example 3 but in lieu of theair driver of FIG. 4, a driver of the character shown in FIG. 10 wasutilized. It was found that the resulting substrate, following cure andsizing in tolerance station 76 exhibited enhanced activated carbongranule retention upon shaking the substrate in an effort to dislodgethe particles therefrom.

EXAMPLE 6

(a) A substrate was manufactured in accordance with Example 3, but inlieu of the air driver of FIG. 4, a particle driver of the charactershown in FIG. 11 was utilized. In this instance carbon loading on theorder of from 304 to 323 grams per square foot was achieved. Retentionof the activated carbon particles in the substrate was very good asmeasured by shaking the substrate following curing and thickness sizing.For example, in checking several samples, between 0.85 and 1.74 grams ofcarbon were lost by the shaking.

Several further samples were made using the processing line illustratedin FIG. 1 to determine the amount of particulate that could beeffectively filled and retained in a substrate and the data is tabulatedbelow. In the table, the substrates measured (before filling) nominally13" by 13" and were of original and final thicknesses as indicated.Original thickness refers to the nominal pad thickness prior to fillingwhile the final thickness is that which it measured following squeezingin the tolerance station 76. The substrates being filled were non-wovenof 200 denier polyester fiber and had a density of 4.4 ounces per squareyard. All substrates were filled from both sides using activated carbonparticles measuring 6/12 U.S. screen series. The series D samples weresubjected to an overcoat on both sides in station 62. Each sample wascured twice once for each side after coating. For comparison purposes,it was calculated that a filled filter one inch thick would containabout 1135 grams per square foot and would have an average pressure dropthereacross of 1.0 inches water column at 200 fpm. The pressure dropmeasurement for the samples was taken by placing two of the samplelayers together and passing air therethrough at 200 fpm.

The term "percent of volume loading" refers to the percentage by volumeof carbon in the substrate after the loading. It is determined inaccordance with the following formula:

    (Specific Volume of Carbon: Specific Volume of Substrate)×100

The basis would be one square foot of substrate one-half inch thick. Forexample: ##EQU1##

    ______________________________________                                        Sample:      A(1)    B(1)      C(1)  D(1)                                     ______________________________________                                        Original     1/2     1/2       1/2   1/2                                      Thickness                                                                     Nom, in.                                                                      Pad, Dry     14.10   14.05     3.44  14.45                                    Wgt. gms.                                                                     Adhesive     42.84   51.24     55.55 65.78                                    Wgt. gms.                                                                     Activated    270.62  300.67    313.18                                                                              314.96                                   Carbon, net gms*                                                              6/12 U.S. Mesh                                                                (granular)                                                                    Shake loss gms.                                                                            2.18    0.54      1.60  0.14                                     Finished thick-                                                                            5/8     5/8       5/8   5/8                                      ness before                                                                   compression in.                                                               % Vol. loading                                                                             38.4    42.6      44.5  44.7                                     before compres-                                                               sion, %(4)                                                                    Finished thick-                                                                            7/16    7/16      7/16  7/16                                     ness after com-                                                               pression                                                                      in.(2)                                                                        % Vol. loading                                                                             54.4    60.5      63.1  63.4                                     after compres-                                                                sion, %(5,2)                                                                  Pressure drop                                                                              .13     .15       .16   .15                                      @ 200 fpm, in                                                                 H2O(6)                                                                        Pressure drop                                                                              .16     .17       .22   .20                                      @ 200 fpm, in                                                                 H2O(7,2)                                                                      Pressure drop                                                                              1.0     1.0       1.0   1.0                                      of 1" thick                                                                   (nom) filled                                                                  filter at 200                                                                 fpm                                                                           ______________________________________                                         *After deducting carbon lost from shaking.                                    (1)A, B, C, and D are averages of 4 samples each.                             (2)Averages of A (3&4), B (3&4), C (3&4), and D (3&4) only, and sized.        (3)A. Samples made with air driver only. B. Samples rolled after air          driver. C. Samples rolled before air driver. D. Samples rolled after air      driver, and overcoated.                                                       (4)Based on 5/8" thickness before compression.                                (5)Based on 7/16" thickness before compression.                               (6)2 layers in 1" frame before compression.                                   (7)2 layers in 1" frame after compression.                               

From the foregoing chart, it may be determined that with the driver ofthe type shown in FIG. 4, it was possible to suspend the equivalent ofabout 48 percent of the activated carbon in the substrate as comparedwith the carbon weight of a filled filter of the same thickness. Wherethe substrate was filled using the driver of FIG. 10, approximately 53percent of the carbon, by weight, could be suspended in the substrate ascompared with the carbon in a comparable size filled filter. Finally, ina substrate which was filled using the driver of FIG. 11, approximately55 percent of the carbon weight of a filled filter could be suspended inthe substrate. At the same time, the table shows that the pressure dropacross the samples was between 13 percent and 22 percent of the pressuredrop of a comparable filled filter

Utilizing the substrate filling techniques above-described, a substratewas made up using a pad of non-woven polyester with a denier of 30 and adensity of 3.6 ounces per square yard and filled with 20/50 (U.S. Mesh)activated carbon particles. Only one side of the substrate was filledwith carbon and an overcoat was provided to insure locking of the carbonon the substrate. This resulted in a filter substrate which would besatisfactory for domestic range hood use. The amount of carbon can becontrolled quite accurately by regulating the blow-off provided by thefilling step. The filling may be accomplished by utilizing the driver ofFIG. 4. This product will provide quite an efficient filter because ofthe small size carbon grains being used.

A relationship exists between the effectiveness of the overcoat instation 62 in locking the particles in place and the density and denierof the substrate itself. As the particle size of the media increases,the overcoat provided in station 62 becomes less effective to hold theparticles in place. If sufficient adhesive is applied to retain thelarger particles the adhesive tends to coat the surface of the activatedcarbon particles so that the carbon is less effective to absorb odors.The capacity of the carbon may not be reduced but the efficiency isdiminished by the overcoat.

In those instances where a substrate is filled at both sides to providethe maximum loading of the substrate with the odor-removing media, thefilter is normally intended for a commercial/industrial use and in thisinstance, high-efficiency is generally required. Therefore, in thoseinstances, an overcoat may not be desired because the efficiency of thefilter is to be maintained at the highest level. In such cases thefilter substrate may be enclosed in the scrim envelope shown in FIG. 7.

Thus, it has been determined that with large activated carbon particlessuch as 4/6 U.S. Mesh on a high denier mat such as 250 to 300 denier, ormore, and where high efficiency is desired, an overcoat as provided bystation 62 may not be desired. However, with high carbon loading (100grams to 500 grams per square foot) the overcoat provided by station 62may enable the manufacture of the filter without the use of the scrimenvelope as shown in FIG. 7.

The second or overcoat provided by station 62 is desirable when it isintended to effect better particle- to-particle or particle to substratebonding and to minimize shedding or defoliation of the carbon particles.The overcoat may be particularly beneficial a) where there is a smalldenier mat with small mesh carbon, i.e., 20/50 (U.S. Mesh); b) wherethere is an essentially impervious substrate with larger carbonparticles such as 6/12 (U.S. Mesh); or c) where a high carbon loading isintended (such as 100 grams to 500 grams per square foot), and it isdesired to avoid the use of the scrim cover as in FIG. 7.

It has also been found that the overcoat provided by station 62 in FIG.1 is particularly useful where the carbon or odor removing media are nolonger regularly shaped, but are irregular in configuration. In suchinstance the irregular configuration appears to lend itself well to theparticle to particle or particle to fiber bonding or particle tosubstrate surface bonding provided by the overcoat of station 62.

As indicated above, it has also been found that improved adhesivebonding between the odor-removing particles and the substrate iseffected without the overcoat where the driving techniques of eitherFIG. 10 or FIG. 11 is utilized, i.e., where the carbon or odor-removingparticles are worked in the substrate by the rollers.

In FIG. 16 a modified form of the method for producing the odor removingsubstrate of FIGS. 5-8 is disclosed. In this method, instead of sprayingthe substrate to apply the adhesive as in station 34 of FIG. 1, thesubstrate S' is passed through a roll coating station 34' having a rollcoater 100 of conventional construction as in U.S. Pat. No. 4,227,904,to which adhesive may be fed from an adhesive reservoir 102. It has beenfound that a suitable adhesive for this type application is a styrenebutadiene synthetic latex and may be purchased from Chemical TechnologyInc, Detroit, Mich., grade #CTI-2004.

It has been found that by roll coating the substrate S' instead ofspraying it, the same adhesive loading may be achieved with less than50% or more of the adhesive used in spraying. In addition, the problemsof handling and disposing of the water pollution which occurred in thewater trough 36 of FIG. 1 are completely eliminated, air pollution isessentially eliminated and as a result potential health hazards areavoided.

It has been found that the roll coating serves to work the adhesive downinto the substrate through the squeezing action of the rollers againstthe upper and lower surfaces of the substrate whereby the adhesivepenetrates the substrate more effectively than where the adhesive isapplied by spraying. It has been found that by adjusting the verticaldistance between the rollers to squeeze more or less the substrate,penetration of the adhesive into the substrate may be varied from merelya surface coating (where little squeezing is effected) to penetrationdown to about the center of the substrate (where greater squeezing iseffected). If it is desired to impregnate the substrate with adhesivecompletely therethrough, it is necessary to roll coat both sides of theadhesive as hereinafter mentioned.

From the roll coater the substrate S' is deposited on a conveyer 104upon which it passes to the particulate filling station 44' beneath thehopper 46' containing the particulate media to be loaded into thesubstrate. The hopper corresponds to that shown at 46 in FIG. 1. Thesubstrate, after moving beneath the hopper and having the particulatemedia deposited thereon, may optionally move beneath particulate drivermeans 54' shown in FIGS. 1 and 4 for driving the particulate down intothe substrate where such is desired. Alternatively the drivers of eitherFIGS. 10 or 11 may be used as desired.

It has been found that the combination of roll coating the adhesive onthe substrate S' and the working of the particulate against the adhesivein the substrate by the drivers of FIGS. 4, 10 or 11 results in asubstrate that will retain the particulate media very effectivleywithout the need for a second adhesive coating as in station 62 ofFIG. 1. Accordingly, filters made using roll coating of the substrateand the particulate drivers of FIGS. 4, 10 or 11 do not require anyovercoating.

From the filing station the substrate moves to a conveyer 110 disposedin the drying station and passes beneath a drying means 112 which,unlike the curing station 74 of FIG. 1 may comprise a manifold withdownwardly directed orifices therein to which heated air is fed so thatthe heated air is applied downwardly evenly across the upwardly facingsurface of the particulate coated substrate. It is intended that theadhesive be cured at this point sufficiently so that it may be handledwithout contaminating the handler. It may not be completely cured atthis point. The adhesive will continue to cure at room temperaturefollowing the drying station until completely cured. Downstream of thedrying station is a tolerance station similar to that shown anddescribed at 76 in FIG. 1.

In FIG. 17 there is shown a filter assembly 120 utilizing a substrate132 manufactured as disclosed in FIG. 16. The filter assembly includes aframe 122 formed of paper, metal or other material providing somerigidity to the assembly. The frame comprises an encircling U-shapedchannel 124, (see FIG. 18) connected across opposite faces of the filterby cross members 126 and 128. Within the frame is a sandwich filtercomprising a 3/4" prefilter substrate 130 which comprises a 40 denier,non-woven polyester fiber mat. Juxtaposed against the prefilter is a3/4" substrate made on the processing line of FIG. 16 and comprising a40 denier non-woven fibrous mat substrate 132 which has been filled withactivated carbon particles such as 6/16 U.S. mesh in 30 to 60 activityat the rate of anywhere from 100-300 grams per square foot. The mat wasfilled from both sides, i.e, the substrate was run through the line ofFIG. 16 twice, first with one face uppermost and then inverted with theopposite face uppermost. Juxtaposing the lower face of the filled mat isan expanded metal screen 134 to give added rigidity to the structure,and beneath that is a reticulated foam layer 136 for catching any carbonparticles tending to shed from the assembly. In use, air flow isindicated by the arrow in FIG. 18. This structure provides a lowpressure drop filter. If a greater pressure drop can be tolerated, as byincreasing the width or number of the cross members 126 and 128, theexpanded metal screen 134 may be eliminated.

In FIG. 19, a prefilter pad 130' similar to that shown in FIG. 18 isprovided on top of a particulate loaded substrate 132' and surroundingthe bottom face and edges of the substrate 132' is a reticulated foamlayer 136' which is secured, as by adhesive at the sides 138 to theedges of the prefilter layer 130'. In the FIG. 19 structure the assemblyis generally flexible and shedding of carbon particles from substrate132' is prevented on one face by the prefilter 130' and on the otherface and at the edges by the reticulated foam 136'. The filter of FIG.19 would be placed in a suitable supporting structure during airtreating use.

In the FIG. 20 arrangement a prefilter pad of 40 denier materialindicated at 130" is coated on one side with particulate carbon and thecoated face 140 of the pad is covered by a reticulated foam layer 136"which is carried up around the edges and adhesively secured to suchedges of the substrate 130". Thus, that face of pad 130" bearing carbonparticles is covered by the reticulated foam to prevent shedding. Thesubstrate 130" shown in FIG. 20 is desirably manufactured on the lineshown in FIG. 16 where but one side of the pad is coated. This typefilter may be on the order of 1" in thickness or conceivably less andwould be normally placed in a supporting frame for use in a filteringprocess.

It is to be understood that FIGS. 19 and 20 are simply cross-sectionsthrough the edge of filter structures made according to this inventionand as described above.

What is claimed is:
 1. The method of making an odor removing thin bedfilter comprising the steps of:supporting an air permeable substratehaving pores or voids therein in a generally horizontal position;applying adhesive to the upwardly disposed face of the substrate anddown into the substrate; depositing particles of an odor removing mediain a layer several particles deep on the upwardly disposed face of thesubstrate; physically pressing the deposited media down into thesubstrate while physically working it into the pores or voids andagainst the adhesive therein to distribute the media over the surfaceand down into the substrate below the surface of the substrate andeffect contact with the adhesive and with surfaces of the pores or voidswithin the substrate; and curing the adhesive on the substrate to lockthe media therein.
 2. The invention defined by claim 1 wherein theadhesive is applied to the substrate by either spraying or roll coating.3. The invention defined by claim 1 or 2 wherein the media is presseddownwardly into the substrate by passing a roller over the upwardlyfacing surface of the substrate arranged to press and work the mediadown into the substrate.
 4. The invention defined by claim 1 or 2wherein following the pressing of the media downwardly into thesubstrate and prior to curing, again applying adhesive to the upwardlydisposed face of the substrate.
 5. The invention defined by claim 4wherein an air jet is directed against the upwardly facing surface ofthe substrate prior to curing the adhesive to remove excess mediatherefrom.
 6. The invention defined by claim 1 or 2 wherein an air jetis directed downwardly against the upwardly disposed face of thesubstrate to press the media downwardly into the substrate.
 7. Theinvention defined by claim 6 wherein an air jet is directed at the odorremoving media deposited on the upwardly facing surface of the substrateto press the media into the substrate and blow off excess media on theupwardly facing surface.
 8. The invention defined by claim 1 wherein theadhesive is cured with heat and following curing of the adhesive, andwhile the adhesive is still warm, pressing downwardly against theupwardly facing surface of the substrate to size the thickness of thesubstrate.
 9. The invention defined by claim 1 or 2 wherein followingcuring of the adhesive the substrate is encased within an air permeableenvelope for retaining odor removing media which may become loosenedfrom the substrate.
 10. The invention defined by claim 1 whereinfollowing curing of the adhesive the substrate is inverted to disposethe other face upwardly and the method is repeated.
 11. The inventiondefined by claim 1 wherein the substrate is placed on a conveyor withone face disposed upwardly and is moved through the several steps on theconveyor.
 12. The invention defined by claim 1, wherein theodor-removing media particles have a size sufficiently small to bereceived within the interstices of the substrate and sufficiently largenot to percolate directly through the substrate.
 13. The invention ofclaim 12 wherein the pressing of the media is sufficient to distributethe media substantially uniformly through the thickness of thesubstrate.
 14. The invention defined by claim 12 wherein the pressing ofthe media into the substrate is sufficient to distribute the mediathroughout about one-half the thickness of the substrate.
 15. Theinvention defined by claim 1 or 2 wherein the substrate comprises anon-woven web and the particles are pressed into the web by directing anair stream against the particles lying on the upwardly facing surface.16. The invention defined by claim 1 or 2 wherein the substratecomprises a non-woven web and the particles are pressed into the web bypassing a roller over the web arranged to engage and press the mediadown into the substrate.
 17. The invention defined by claim 1 or 2wherein the substrate comprises a woven mat of small denier strands andexcess particles are removed from the mat by directing an air jetagainst the particles on the mat.
 18. The invention defined by claim 3wherein just prior to passing a roller over the upwardly facing surfaceof the substrate, an air jet is directed at the surface of the substrateto remove excess particles on the substrate and drive particles downinto the substrate.
 19. The invention defined by claim 3 whereinimmediately following passing of the roller over the upwardly facingsurface of the substrate, and prior to curing of the adhesive, an airjet is directed against the surface of the substrate to blow off excessparticles thereon.
 20. The invention defined by claim 3 whereinfollowing pressing of the media into the substrate and prior to curingthe adhesive, excess media is blown off the upwardly disposed face ofthe substrate.
 21. The invention defined by claim 20 wherein followingblowing of excess media off the substrate and prior to curing theadhesive, again applying adhesive to the upwardly disposed face of thesubstrate.
 22. The invention defined by claim 3 wherein followingdeposit of particles of odor-removing media on the substrate, blowingexcess media off the substrate and thereafter pressing the media intothe substrate and again apply adhesive to the upwardly disposed face ofthe substrate.
 23. The method of making an odor-removing thin bed filtercomprising the steps of:supporting an air-permeable substrate havingpores or voids therein in a generally horizontal position; applyingadhesive to the upwardly disposed face of the substrate; depositingparticles of an odor removing media in a layer several particles deep onthe upwardly disposed face of the substrate; directing an air jetagainst the upwardly disposed face of the substrate and against themedia to drive the media down into the pores or voids and also to removeexcess media from the surface of the substrate; again applying adhesiveto the upwardly disposed face of the substrate; and curing adhesive onthe substrate to lock the media on the substrate.
 24. The inventiondefined by claim 23 wherein the adhesive is applied to the substrate byspraying.